Investigators release details of deadly WC-130 crash

The Air ForceWC-130H aircraft veered to the left on the runway, almost rolling into the grass before the crew was able to get it airborne.

The pilot quickly made the decision to return to the Georgia airfield they had just departed. The pilot directed the shutdown of engine one, operating on the remaining three.

"Coming back," the pilot repeated five times over the next 30 seconds.

Investigators said that within those few seconds the pilot improperly applied nine more degrees with the left rudder, "which resulted in a subsequent skid below three-engine minimum controllable airspeed, a left-wing stall, and the [mishap aircraft's] departure from controlled flight."

No other "meaningful direction" was given to the crew other than an order to "brace" just before impact.

The plane was airborne for two minutes overall before it crashed down into Georgia State Highway 21 roughly 1.5 miles northeast of the Savannah/Hilton Head International Airport, killing all aboard.

A newly released mishap report determined that the WC-130 crash that claimed the lives of nine members of the Puerto Rico Air National Guard in 2018 was largely due to pilot error. But troubling engine and maintenance issues documented in the aging aircraft raise more questions about the cause of the catastrophic May 2, 2018 mishap.

The crew should have more closely followed emergency procedure and called for immediate action after discovering one of the aircraft's engines was malfunctioning, Millard said. Instead, the malfunction led to loss of control of the plane, causing it to crash, the report found.

Experts who spoke with Military.com, however, pointed out that lapses in maintenance deeply disadvantaged the crew even before the aircraft left the runway. The plane, which had been in service more than 50 years, was on its final journey to the "boneyard" at Davis-Monthan Air Force Base, Arizona when it went down.

"The engine malfunction is most definitely large factor and I would say the catalyst for the events that unfolded," said an Air Force instructor pilot who flies a mobility aircraft and agreed to speak to Military.com on background about the report's findings. "It appears the [report] narrowed in on a particular piece of the engine (the valve housing assembly) which had intermittent issues with [revolutions per minute] over its lifetime with multiple different engines."

The Air Force ordered an immediate investigation into the accident. Days later, after Military Times published an in-depth report showing that military aviation accidents have increased over the last five years, the service directed its wing commanders to hold a one-day pause in order to conduct a safety review with airmen, assessing trends and criteria that may have led to the recent rash of crashes.

Unsolved maintenance problems

The newly released investigation shows that the plane was cleared for flight even though the recorded oscillation data of the plane's outermost left engine did not match its intended performance.

The WC-130 made its ferry flight from Puerto Rico to Savannah, Georgia, on April 9, 2018. And the flight crew operating the [mishap aircraft] "experienced an RPM issue with engine one, and reported the incident for troubleshooting and repair," the report said.

While the crew found a fix, maintainers struggled to replicate both the in-flight operations and the solution the pilots used to better understand the what went wrong. They found they couldn't recreate the crew's original solution, which was to switch "on the propeller governor control to mechanical governing," to see if that rectified the issue, it said.

A U.S. Air Force Lockheed C-130E-LM Hercules (s/n 64-0510) from the 198th Airlift Squadron, 156th Airlift Wing, Puerto Rico Air National Guard, prepares to take off from Muniz ANGB, Puerto Rico, on Feb. 29, 2004.

According to post-mishap interviews, during a second maintenance engine run, the "mishap maintainers observed engine one produced 99% revolutions per minute," the report said.

But the digital flight data recorder (DFDR) said otherwise.

The DFDR indicated "engine one never reached sustained RPM above 96.8% and had significant oscillations between 95% and 98%," it said.

The Air Force investigators said that when performing an engine run, the [technical order] requires a range "of 99.8% to 100.02% RPM, as displayed on a precision tachometer, to verify an engine is operating properly at 100%.2."

The maintainers, who failed to use a precision instrument, missed a chance to diagnose a fluctuating, weaker engine.

"Good enough" mentality

The maintainers should have noted these red flags, the instructor pilot who spoke with Military.com said.

"The maintainers... failed to properly conduct the inspection of the engine," the instructor pilot said. "The crew likely would have never stepped to the aircraft that day, at least not without the engine being verified to have reached the required power threshold, versus over 2 percent lower than the minimum."

In the report, maintainers are faulted for having a "good enough" mentality about the aircraft's condition.

Twitter user @MikeBlack114, a self-identified Air Force aircraft maintenance officer, also faulted the "good enough" mentality as a reason mistakes were made in a tweet thread. Furthermore, leadership should have paid better attention, he said.

"I'll let someone with wings address the aircrew piece, but the mx [maintenance] portion is almost unfathomable," Black said in a Twitter thread. "If you're in a leadership position of an organization involved with flying and you aren't uncovering the skeletons (believe me, they're there, just a question of how severe they are) you aren't looking hard enough."

Another problem, according to the report, was the maintainers observing the aircraft did not use a tachometer to justify the data.

The report noted that they had conducted the engine test runs without the instrument because the compatible adapter plug to connect the precision tachometer to the aircraft was not available.

"During the engine runs and without the use of a precision tachometer, [mishap maintainer one] and [mishap maintainer two] knew that 100% RPM was the speed the engine should operate at, but believed 99% was sufficient to conclude their maintenance because of the wider gauge range provided in the [technical order]," the report said. "Thus, the mishap maintainers never corrected the engine one discrepancy and did not resolve the RPM issue."

On May 2, 2018, engine one's RPMs once again revealed an anomaly.

During takeoff, engine one's RPMs fluctuated and couldn't be stabilized when the first mishap pilot "advanced the throttle lever into the flight range," according to the report.

While the banked turn the pilots made into the failed engine "was well below the minimum air speed needed for proper control of the aircraft, the [mishap aircraft] did still have enough airspeed to maintain flight," the report said.

"The crew put the aircraft in a disadvantageous energy state by rotating (lifting off) 5 knots early and failing to accelerate as required by the procedures," the instructor pilot said. "Unfortunately, this was not an unrecoverable situation by any means, and one crews in all airframes train to regularly."

The reason for the initial flight in April 2018 was to conduct routine in-tank fuel cell maintenance in Georgia. The 165th Airlift Wing at Savannah Air National Guard Base had the means to do this, unlike the Puerto Rico Guard's 156th Wing.

Puerto Rico's facilities sustained substantial damage during Hurricane Maria and could not offer the maintenance at home station, the report said.

Transparency needed

Although Adjutant Gen. Isabelo Rivera, the commanding officer of the Puerto Rico National Guard, said at the time of the crash the aircraft was more than 60 years old and one of the oldest C-130s in the fleet, its history and maintenance record say otherwise.

The aircraft, tail number 65-0968, rolled off the assembly line in 1965 as a standard C-130E, its records show.

Aircraft 65-0968.

"Sometime in the early 1970's, it was converted to a WC-130H for use in weather reconnaissance (the "W" designation indicates the weather modifications)," the report said.

The engines were also "upgraded from T56-A-7 to the T56-A-15 at that time (which changed the "E" designation to "H")," it said.

The aging aircraft life was extended because the wing had been expected to change missions. But that transition never came.

The fiscal 2016 budget "initially divested the six WC-130H aircraft from the Puerto Rico Air National Guard "and provided direction to move the 156th Airlift Wing to the RC-26, a manned Intelligence, Surveillance, and Reconnaissance (ISR) platform," the report said. "However, this direction did not prove viable, as there was no requirement for a manned ISR mission in the United States Northern Command Theater."

Millard, the investigator, said in the report there were no outstanding time compliance technical orders that would have restricted the plane from from flying.

Still, there should have been more transparency, the instructor pilot said.

"As an aircraft commander, there's a 'trust but verify' mentality with the maintenance crews, but our knowledge is limited. So when a crew chief hands me the signed forms," he said, "I have to trust those procedures and previous discrepancies have been fixed in accordance with the maintenance technical orders."

This article originally appeared on Military.com. Follow @militarydotcom on Twitter.